1. The feature at A is the mid-ocean ridge. It is an underwater mountain range formed by volcanic activity where new oceanic crust is created as magma rises from the mantle and solidifies.
2. At B, seafloor spreading is occurring. Magma rises from the mantle at the mid-ocean ridge, erupts onto the ocean floor, and cools to form new oceanic crust. This process pushes the existing oceanic plates apart, causing the ocean floor to widen over time.
3. As new material rises from the mantle and forms at the ridge, older material is pushed outward and away from the ridge. Over time, this older material becomes colder, denser, and eventually sinks back into the mantle at subduction zones.
4. Three kinds of evidence supporting seafloor spreading are: (1) Magnetic striping on the ocean floor showing symmetrical patterns of normal and reversed polarity on either side of the ridge; (2) Increasing age of oceanic rocks with distance from the mid-ocean ridge; (3) Thickness of sediment increasing with distance from the ridge, indicating older crust has had more time to accumulate sediment.
5. The process shown at C is subduction. It occurs because the oceanic crust, after moving away from the ridge, cools, becomes denser, and eventually sinks beneath a less dense continental plate or another oceanic plate due to gravity and plate tectonic forces.
Parent Tip: Review the logic above to help your child master the concept of sea floor spreading worksheet.
